Reconstruction of anterior cruciate ligaments

ABSTRACT

Apparatus for locating an attachment position for a reconstructed anterior cruciate ligament on an attachment surface of a bone comprises locating means  51, 61  arranged to locate at least one reference surface  4  of the bone and guide means  53, 54  arranged to define the attachment position in two dimensions on the attachment surface relative to the reference surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No.12/225,460 filed on Dec. 4, 2008, the disclosure of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the reconstruction of the anteriorcruciate ligament, and in particular to the location of attachmentpoints for the reconstructed ligament.

BACKGROUND TO THE INVENTION

The anterior cruciate ligament (ACL) originates from the medial aspectof the lateral femoral condyle and is inserted into the tibial plateaumedial to the anterior horn of the lateral meniscus.

The ACL is a strong structure that has an important role in stabilisingthe knee. It is often injured, especially during sports activities, anddoes not usually heal. Because of these factors, it is usual for aruptured ACL to be treated by reconstructive surgery, when a tendongraft is usually used to replace the damaged ACL. In conventional ACLreconstruction, a single graft structure is made: either a strip of thepatellar tendon, or else a composite structure consisting of usuallyfour strands of hamstrings tendons are used. This graft is placed insidethe knee joint, replacing the ACL. It is hoped that it will heal inplace and remodel into a new ACL.

In order to fix the new graft in place, it is usual for the surgeon todrill a graft tunnel at the attachment site in both the femur and tibia.These tunnels are usually placed at the anatomical attachment areas ofthe damaged ACL. During surgery, the graft is pulled into these tunnelsand secured; many devices have been developed to anchor these grafts.

The principal reason for ACL reconstructive surgery to fail ismalplacement of the graft fixation tunnels. That occurs because the ACLis placed awkwardly within the knee joint, and it is difficult to judgethe exact positions needed, even when looking through a modernarthroscopic camera system. Recognising this, surgical instruments haveevolved to try to make the choice of tunnel position less subjective,but that approach has not developed to the point where errors areavoided.

A further factor is that the ACL has a complex fibre bundle structure,with many fibre fascicles that attach over quite large areas on the bonesurfaces. This leads to individual fibres having different lengths. Theyalso have different patterns of tightening and slackening as the kneeflexes and extends, or as the tibia rotates about its long axis.Recognising this, there has recently been a development of‘double-bundle’ reconstruction methods. This usually involves making twotunnels in each bone, and using two grafts. These are a crudeapproximation of two main areas of fibres in the cross-section of theACL [Fakhry G &.Girgis. T. Clin Orthop 1975; 106]. These bundles arenormally called the ‘anteromedial’ AM bundle (or AMB) and‘posterolateral’ PL bundle (or PLB). These names relate to theirrelative positions of attachment to the tibial plateau. In general, ithas been found that the PLB tightens as the knee is extended, while theAMB is tightest in the flexed knee [Xerogeanes J W. et al. Knee SurgSports Traumatol Arthrosc 1995; 3: 9-13, Sakane M. J Orthop Res. 1997;15: 285-293, Bach J M. et al. J Biomech. 1997; 30: 281-283]. Thus, theyhave distinct stabilising roles. The underlying principle ofdouble-bundle surgery is that it more closely reproduces the natural ACLanatomy, and also functions closer to the natural ligament than does asingle-bundle reconstruction. Isometric reconstructions reproduce theanteromedial bundle, but the knee needs stability in the functionalposture, which is when it is weight-bearing near extension, ie theposterolateral bundle is then needed.

Surgical methods of ACL reconstruction following injury have developedconsiderably over the last 15 years. Primary repair and extra-articularprocedures have failed to reproduce satisfactory stability of the knee[Grontvedt T. et al. J Bone Joint Surg [Am] 1996;78-A: 159-68] and theuse of prosthetic ligaments has been abandoned [Frank C. & Jackson D W.J Bone Joint Surg [Am] 1997;79-A:1556-76]. These techniques have beensuperseded by reconstruction with an intra-articular graft. Hence, thecurrent surgical approach is by anatomical reconstruction using abiological tissue autograft. The bone-patellar tendon-bone graft B-PT-Bhas given good clinical results [Corry I. S. et al. Am J Sports Med1999;27:444-53] but morbidity at the donor site [Christen B. & Jakob RP. J Bone Joint Surg [Br] 1992;74-B:617-19, Kartus J. et al. Knee SurgSports Traumatol Arthrosc 1997;5:222-8] has prompted many surgeons tofavour a four-strand hamstring graft, usually using the tendons ofsemitendinosus and gracilis doubled.

Radford and Amis [J Bone Joint Surg Br 1990; 72: 1038-1043] reportedthat a double-bundle reconstruction controlled anterior laxity betterthan single-bundle reconstructions, across the range of knee flexion.Yagi et al [Am J Sports Med. 2002; 30: 660-666] reported finding thebiomechanical outcome, especially in rotatory loading, may be superiorwith double bundle reconstructions compared to single bundlereconstructions, and Mae et al [Arthroscopy 2001; 17: 708-716] similarlyfound better antero-posterior stability using a two femoral sockettechnique when compared to the standard single socket ACLreconstruction. Mommersteeg et al [J Anat. 1995; 187: 461-471] suggestedthat successful ACL reconstruction may not be achieved simply byreplacing one bundle. Conventional endoscopic ACL graft placement doesnot always control tibial rotation laxity, leaving a residual‘mini-pivot’ [Bull A M J. et al. J Bone Jt Surg 84Br: 1075-1081, 2002].The realisation that anterior laxity is not an adequate measure ofsuccess of an ACL reconstruction, and that rotatory laxity is importanthas led to a sudden widespread interest in double-bundle methods, [AmisA A et al. Operative Methods in Sports Med 15; 29-35, 2005].

Race & Amis developed a double-bundle PCL reconstruction method [J BoneJt Surg 80B, 1998; 173-179] that was widely adopted, partly because itwas also shown clearly that: a) the PCL was not an isometric ligament;b) that isometric PCL reconstructions gave less effective control oftibial posterior laxity.

ACL reconstruction aims to recreate the exact mechanical properties ofthe injured ligament and restore normal function to the knee. Currently,this cannot be achieved. Biomechanical testing of ligamentreconstructions in the laboratory has been used widely in attempts torecreate these mechanical properties. Although the ultimate load tofailure of the B-PT-B and that of the four-strand hamstring graft exceedthose reported for the intact ACL, it is accepted that in the earlypostoperative period it is the fixation of the graft which is the weaklink [Kurosaka M. et al Am J Sports Med 1987;15:225-9].

ACL fixation may be either mechanical or biological. The emphasis onaccelerated programmes of rehabilitation and demands for a rapid returnof function necessitate secure mechanical fixation in the earlypost-operative period before biological fixation has occurred by healingin the graft tunnel.

As ACL reconstruction techniques evolve, an accurate and usefuldescription of the attachment anatomy is required in order to designinstruments capable of placing graft tunnels so that their entrances arein anatomically correct locations, within the ACL attachments.Anatomical descriptions of the attachment anatomy of the two bundles ofthe ACL using methods that can be employed clinically are lacking. Anaccurate map of the attachment of the ACL on the femur is key for thedevelopment of double bundle techniques and in outcome studies todescribe optimal and suboptimal positions for graft placement.

The importance of femoral tunnel placement in ACL reconstruction haspreviously been reported with respect to a single graft bundle technique[Amis A A. & Jakob R P. Knee Surg Sports Traumatol Arthrosc 1998; 6Suppl 1: S2-12]. Sommer [Knee Surg Sports Traumatol Arthrosc 2000; 8:207-213] found a significant correlation between the femoral singlebundle placement and the International Knee Documentation Committee IKDCscore. As the placement of the graft as seen on X-ray moved away fromthe most isometric point, the IKDC scores decreased. It will be just ascritical to achieve optimum graft placement in the double bundletechnique as it is in the single bundle technique.

EP0361756 describes a device that measures changes in distance betweenchosen points on femur and tibia. It does not assist the surgeon inidentifying anatomical locations for graft tunnels; instead it helps toidentify points that are a constant distance apart when the knee flexesi.e. points that are “isometric”.

EP0440991 A1 also refers to finding an ‘isometric’ point. It alsodescribes a new type of drill for making a hole of known depth. A tibialdrill guide is also described. However this device relies entirely onthe surgeon's judgement for placement within the knee. A feature of thisdevice is that the guide barrel can slide towards the bone until itssharp tip engages the bone, thereby stabilising the drill guide in thechosen position. This feature is common to many types of drill guides.

EP0495487 A2 discloses a drill that, instead of just boring out a holethrough the bone, cuts it out as a solid core, for use elsewhere in theoperation. A “guide for locating a pilot hole on the femoral condyle” iscited but this is a bone coring/drilling method, there is no assistancegiven to place the tunnel accurately.

U.S. Pat. No. 4,883,048 discloses a feature that is used widely, namelythe use of an arcuate feature to allow the drill to be guided through atube to a fixed point from a range of directions. However, the choice ofprecisely where to drill is still surgeon-dependent; the instrument doesnot locate the optimal site.

U.S. Pat. No. 5,269,786 and U.S. Pat. No. 5,409,494 use the arcuatefeature. They describe a drill guide that does aim to locate the correctplace for a graft tunnel, but it does so by locating on anotherligament, the PCL, and does not utilise bony features. The PCL is a softtissue structure and so is inherently inaccurate as a datum.

In U.S. Pat. No. 6,019,767 and U.S. Pat. No. 5,300,077 is described adevice whose principle is that the axis of the drill guide is alignedparallel to the probe tip that rests on the roof of the femoralintercondylar notch. Thus, it ensures that the graft will not impingeagainst the notch roof. It therefore locates the tibial drill hole inrelation to the femur. It does not address the femoral tunnel location.

U.S. Pat. No. 5,350,383 also uses the arcuate feature but attempts to‘invert’ the moving feature. Once again the surgeon judges where toplace the drill target.

U.S. Pat. Nos. 5,520,693, 6,352,538 and 6,878,150 give a device that hasa tongue protruding from the body of the drill guide that locates on anedge of the bone, ensuring that the drill axis is located a certaindistance from that edge. However, it does not identify where to go alongthe edge of the bone—only one direction/dimension is controlled. Thesurgeon usually places the probe or tongue at a chosen “o'clock”position in the femoral notch.

U.S. Pat. No. 5,603,716 describes a means of locating tunnel positionsusing an aimer referenced to anatomical structures within the knee. Itis a method for drilling a socket in the tibia but it does nothing toidentify exactly where the socket should be situated.

The devices provided by U.S. Pat. No. 6,254,604 and U.S. Pat. No.6,254,605 are similar to U.S. Pat. No. 5,300,077 but the latter adds aremovable guide bar to provide visual alignment in the coronal plane.This principle being that, if the bar is held horizontal, then the drillguide will slant across the tibia in a preferred orientation. Thisguides the tunnel orientation.

The basis of the device in EP0384098 is that it combines two drillguides in one instrument, with a fixed relationship between them,intending to create tibial and femoral tunnels at the “correct” placesin the knee. It has a hook that locates over the posterior edge of thetibia. The tibial tunnel is always on the midline while the femoraltunnel guide can be swung to left or right for an oblique tunnel in leftor right knees. The femoral tunnel is located in relation to the hook onthe tibia.

GB 2 268 688 provides a device for locating tibial tunnels. The deviceis simply placed into the knee at an angle to the midline plane, so thatits probe passes to one side of the patellar tendon. Bends areintroduced into the instrument, to allow the probe tip to be straightalong the midline plane, while the body of the drill guide is held at anoblique plane outside the knee.

U.S. Pat. No. 4,257,411 describes a drill guide adapted to clampsecurely onto the bone. It has no features that locate the tunnel inrelation to the anatomy.

U.S. Pat. No. 5,112,337 describes a further device for tibial tunnelplacement. It relies on surgeon's judgement of where to drill the hole,by placing a target tip. It has an arcuate adjustment to vary the tunnelorientation. It also allows the drill guide to slide until its tipengages the bone. The sliding drill guide has length marks so that thesurgeon can choose a desired tunnel length.

U.S. Pat. No. 4,823,780, EP0162027 and U.S. Pat. No. Des 289,436 providea device for making tunnels that are in a fixed relationship in space.The device requires surgeon's judgement for placing it correctly in theknee, it has no location features.

A study of graft tunnel positions following endoscopic single-bundle ACLreconstructions performed by surgeons in Europe revealed a need formajor improvement in ACL reconstruction instrumentation, a principal aimbeing to reduce the subjective element of judgement of instrumentpositioning prior to drilling bone tunnels [Kohn D. et al in Knee Surg.Sports Traumatol. Arthrosc. 6 Suppl 1: S13-S15, 1998].

The present invention aims to address two unmet clinical needs: Firstly,the frequent failure of ACL reconstructions, which is mostly caused bymisplacement of the graft tunnels and, secondly, the residual rotatorylaxity remaining after conventional endoscopic ACL reconstruction of theknee.

The inventors have measured the location and extent of the femoral andtibial attachments of the ACL. A range of different measurement systemshas been used, reflecting methods published previously. Some of themeasurement methods have been modified in order to make them morerelevant to arthroscopic surgery. This work included measurement of thecentres of both the entire ligament and also of the individual fibrebundle attachments. The attachment locations have been related to bonelandmarks suitable for locating instruments.

SUMMARY OF THE INVENTION

The present invention provides apparatus for locating an attachmentposition for a reconstructed anterior cruciate ligament on an attachmentsurface of a bone, the apparatus comprising locating means arranged tolocate at least one reference surface of the bone and guide meansarranged to define the attachment position in two dimensions on theattachment surface relative to the reference surface.

The present invention further provides a method of locating anattachment position for a reconstructed anterior cruciate ligament on anattachment surface of a bone, the method comprising locating at leastone reference surface of the bone and defining the attachment positionin two dimensions on the attachment surface relative to the referencesurface.

Some embodiments of the present invention provide novel instrumentdesigns based upon detailed anatomical measurements of the attachmentlocations of the AM and PL bundles of the ACL, which are useful for bothsingle and double-bundle ACL graft reconstructions.

Single-bundle ACL reconstruction is a difficult procedure. Indouble-bundle methods, the need for four tunnels creates greaterpotential for surgical error. Some embodiments of this invention provideaccurate instrumentation, which can reduce or eliminate subjectivejudgement regarding tunnel placement and facilitates double-bundle ACLreconstruction.

This invention relates in part to advancing the art of double-bundlereconstruction surgery. It recognises that it is essential to know thelocations of the bundle attachments, in order to be able to designinstruments that can guide the surgeon to the correct tunnel sites. Thisinvention also applies to the development of software for surgicalguidance ‘navigation’ systems.

It is difficult to provide the relevant geometrical information, becauseof the complex shape of the internal cavity of the knee joint. As aresult of taking many measurements on cadaveric specimens, thisinvention provides several different systems for locating the bundleattachment points. In particular, these measurements are related tovisually identifiable features of the bony anatomy. This is importantbecause the bony anatomy will usually remain with only small changesafter ACL injury, whereas the ACL itself will often disappear if thereis a delay between injury and surgery. These measurements, therefore,provide the basis for designing guidance instruments that locate onto,or in relation to, bony landmarks. This provides a greater degree ofreproducibility than with currently available instruments and avoidssubjective human errors of tunnel placement.

It should be recognised that the measurement data is useful not only forplacing the graft tunnels in double-bundle reconstructions but also forconventional single-bundle procedures. Measurement data for the centresof the whole ACL attachments to both femur and tibia is used in novelinstrument design.

In one embodiment, the invention provides instruments that make use ofanatomical measurement data and the principle of locating off of bonylandmarks. While it is normal to locate conventional femoral drillguides this way, it only works in one direction, not in the necessarytwo-dimensional way. One instrument used in the art is called an ‘offsetdrill guide’ that has a hook-like extension that locates over a ridgeacross the back of the femur. The body of the instrument then guides apin to the desired tunnel location a fixed distance away from the ridge(the offset). It does not, however, control where along this ridge thesurgeon may choose to place the guide.

For the tibia, a further provision of this invention is a surgicalinstrument having a probe that extends posteriorly through the knee, andis bent downwards at its tip. This provides a hook that can locate overa transverse ridge, where the tibial surface slopes down to theattachment point of the posterior cruciate ligament PCL. This featurecontrols the anterior-posterior position i.e. front to back. Themedial-lateral position i.e. left-right when looking into the front of aleft knee is then controlled by locating the side of the probe against aprominent bony spur called the medial tibial tubercle. Thus, thisinstrument controls the tunnel position in two dimensions across thetibial plateau.

For the femur, a further embodiment is an instrument with a probe thatlocates over the posterior transverse ridge, but which also extendsaround the surface of the intercondylar notch where the ACL attaches.This also locates in two dimensions, avoiding subjective assessments ofwhere to place the tunnel around the notch.

A further aspect of the invention is that the surgeon usually looks atwhat is happening via an arthroscope. While that gives a magnified view,it is one-dimensional, so that depth perception is limited. It alsomeans that the surgeon loses sight of how the field of view relates tothe overall alignment of the limb segments, the thigh and shank. Thissituation may cause instruments to be used in a skewed orientation,particularly because the instruments usually enter the knee in aslanting orientation, passing either side of the large centrally-placedpatellar tendon. In order to avoid such misorientation, the inventionincorporates deviations or bends in the shafts of the locationinstruments so that the surgeon can hold them in line with the limbsegments whilst the ‘working’ tips are at the correct posture within theknee joint.

Another aspect of the invention is that the instrument shafts mayincorporate alignment rods that aid alignment, e.g. by being heldparallel to the limb.

Yet another aspect of the invention is that the measurement data enablesa range of instrument sizes of the relevant dimensions to be designed tosuit the range of knee sizes that exist among the general population.This feature enables accurate tunnel placement regardless of individualjoint dimensions.

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a tibial plateau;

FIG. 2 is an anterior-posterior view of a proximal tibia;

FIG. 3 is a sectioned lateral-medial view of the proximal tibia;

FIG. 4 is a diagram showing various dimensions used to define positionson the tibial plateau of FIG. 1;

FIG. 5 shows part of a tibial drill guide according to an embodiment ofthe invention;

FIG. 6 is a side view of the drill guide of FIG. 5;

FIG. 7 is a partially sectioned medial-lateral view of a distal femur;

FIG. 7 a is a view similar to FIG. 7 including a reference grid fordefining ligament attachment positions on the femur;

FIG. 8 is an end view of the femur of FIG. 7;

FIG. 9 is a side view of part of a drill guide according to a secondembodiment of the invention;

FIG. 10 is an end view of the drill guide of FIG. 9;

FIG. 11 is a side view of part of a drill guide according to a furtherembodiment of the invention;

FIG. 12 is a top view of the drill guide of FIG. 11;

FIG. 13 is a top view of part of a drill guide according to a furtherembodiment of the invention;

FIG. 14 is a top view of a drill guide according to a further embodimentof the invention;

FIG. 15 is a diagram of a computer guidance system according to afurther embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a simplified representation of the anatomy of the tibialplateau, that is the top surface of the tibia. This looks down onto thetibial plateau of a right knee: anterior is at the bottom, posterior atthe top, medial to the right and lateral to the left. The main articularbearing areas are the medial tibial plateau 1 and the lateral tibialplateau 2. The head of the fibula 3 is postero-lateral. The plateaux 1,2 are limited in extent towards the centre of the tibia when they reachbony ridges: the medial tibial spinous process 4, and the lateral tibialspinous process 5. There is a trough, or fossa 6, between the spines 4,5, the interspinous fossa. Posteriorly, the PCL attaches in a posteriorattachment area 7 between the medial and lateral plateaux 1, 2.Anteriorly, the ACL attaches in an anterior attachment area 8 within theinterspinous fossa 6. This attachment 8 may be divided into twoattachment areas, where separate fibre bundle attachments are located:one in the anteromedial bundle attachment area 9 and one in theposterolateral attachment area 10. A transverse inter-spinous ridge 11passes between the medial and lateral spinous processes 4, 5, and formsa transition between anterior and posterior-facing slopes on the surfaceof the bone. The patellar tendon 12 is a strong structure passingvertically from the tibia to the patella at the front of the knee.

FIG. 2 shows an anterior-posterior view of the proximal tibia, with themedial 1 and lateral 2 plateaux, the medial 4 and lateral 5 spinousprocesses, the inter-spinous or, sometimes, “inter-condylar” fossa 6,that contains the ACL attachment 8. The transverse inter-spinous ridge11 forms the central ‘skyline’. The patella tendon attaches distally, tothe tibial tubercle 13, and has been omitted from this view.

FIG. 3 shows a lateral-medial view of the tibia after it has beensectioned in a central sagittal plane. The PCL attaches posteriorly in aPCL attachment area 7, the ACL anteriorly in the ACL attachment area 8.Between the ACL and PCL attachments is the transverse inter-spinousridge 11. The medial spinous process 4 is visible beyond the sectioningplane. The tibial tubercle 13 is prominent anteriorly and the patellartendon 12 passes up to the patella.

The ACL fibre bundle attachments may be located using measurementsrelated to identifiable bony landmarks. These have the advantage oversoft tissue landmarks of not being readily deformed or deflected by theapplication of an instrument, a criticism that applies to instrumentsthat register a fixed distance from the PCL for example. A furtheradvantage of using bony landmarks is that they should persist followingACL rupture, even if the ACL remnants disappear, as occurs in chroniccases. FIG. 4 shows a number of possible methods that can be used todefine the position of either the whole ACL attachment to the tibia or,as shown by way of example, the anteromedial fibre bundle, or else theposterolateral fibre bundle. Line 41 is the posterior tibialtrans-condylar axis, which is the line passing through the mostposterior points on the tibial plateau. This may be used as the datumfrom which to define the ACL position in an anterior direction 42.Alternatively, or in addition, the ACL may be located in relation to ananterior datum position 43 at the edge of the tibial plateau bymeasuring the distance 44 posteriorly from this. A preferred method isto locate the ACL by an anterior distance 45 from the transverseinter-spinous ridge 11. The medial-lateral position may be defined inrelation to the overall M-L width 46 of the tibial plateau, as apercentage 47 of this width from the medial edge, for example.Alternatively, the ACL attachment position may be located in relation tolandmarks within the knee, for example by medial-lateral measurement 48from the medial spinous process 4. Because it is difficult to locate thesummit of the process, it is preferable to measure distances laterallyfrom its steep lateral face. Both anterior-posterior and medial-lateralmeasurements are needed to define the ACL attachment position on thetibial plateau.

Referring to FIGS. 5, 6, a tibial drill guide according to a firstembodiment of the present invention is intended to guide the paths ofthe ACL graft tunnels to the desired location on the tibial plateau, onetunnel for a single-bundle reconstruction, two for double-bundles. Thedrill guide comprises an intra-articular probe 51, connected to a handle52 in the form of a shaft. A mounting 62 in the form of another shaftextends at right angles to the handle 52 and supports two drill guides55, 56 which are interconnected by a joining member 63. The probe 51 hastwo guide apertures 53, 54 through its main portion 51 a. It is alsobent through about 45° at its free end to form a locating portion 61 atthe tip of the probe which is angled to the main portion with a locatinggroove 51 b extending across the probe 51 between the main portion 51 aand the locating portion 61. The underside of the main portion 51 a andthe locating portion 61 forms a locating surface arranged to locate onthe transverse inter-spinous ridge of the tibia as described below. Thislocating surface is made up of two parts, one formed on the underside ofthe main portion 51 a and the other formed on the underside of thelocating portion 61. In this embodiment these two parts are angled atabout 45° to each other, but angles from 30° to 75° have been found tofunction successfully, with angles of 60° or less being preferable, andangles of at least 45° being more preferable. Each of the drill guides55, 56 is in the form of a tube defining a drill guide aperture, andeach of the drill guide apertures is aligned with a respective one ofthe guide apertures 53, 54 in the probe 51.

In use, the intra-articular probe 51 will usually enter the knee jointvia a portal at the medial side of the patellar tendon 12. The probe 51is angled at about 45° to the handle 52 so that if the probe is held toextend in the anterior-posterior direction, the handle 52 extends to theside of the patellar tendon 12. It would be possible to use otherportals, lateral to the patellar tendon or through the patellar tendon,with a suitable change of orientation of the handle 52 in relation tothe probe 51. The medial side 51 c of the probe 51 is located by thesurgeon against the lateral aspect of the medial tibial spinous process4, as shown in FIG. 5. The probe is located in the anterior direction bypulling the angled tip 61 until it engages the back of the transverseridge 11 so that the locating groove 51 b is located on the top of thetransverse ridge 11. By this means, the probe 51 is located in bothmedial-lateral and anterior-posterior directions. The drill locatingapertures 53, 54 are placed to receive the tips of guide wires which arealigned by being passed up through the drill guides 55, 56 and drilledup through the tibia, emerging in the correct locations within the ACLbundle attachment areas 9, 10. The drill guide tubes 55, 56 in this caseare attached to handle 52 in a fixed relationship. However, they may beadjustably attached so that the angle at which the guide wires aredrilled into the tibia can be adjusted. The drill guide tubes 55, 56 arein this embodiment mounted at a compound angle with respect to theanterior-posterior and longitudinal axes of the tibia, i.e. they are atan angle to both of these axes, orientated typically 30 to 70 degreesmedial to the anterior-posterior axis and elevated typically 40 to 60degrees from horizontal, a typical configuration being indicated foranteromedial 55 and posterolateral 56 drill guides in FIGS. 5 and 6.

The drill guides 55, 56 are shown in FIG. 6 with a fixed relationship tothe handle 52 and probe tip 61 via the mounting 62 and joining member 63by way of example only. Adjustment means could allow, for example, theguides 55, 56 to move axially towards the tibial surface, or even toengage the bone using sharpened tips. Alternatively, the orientationscould be adjustable so that they can be altered, by means of a pivotingmechanism that ensures that the axes of the guide tubes always pointtowards the correct points on the surface of the tibial plateau, withinthe ACL bundle attachment areas 9, 10 and the guide apertures 53, 54.

In a modification to the embodiment described above, the drill guide isarranged for a single bundle reconstruction. In this case the probe 51only requires a single guide aperture, and only a single drill guide isneeded, which again can be fixed or adjustable in position.

FIGS. 7 and 8 show the gross anatomy of the right distal femur. FIG. 7is a medial-lateral view, with the bone sectioned on the midline, sothat the medial condyle has been removed. The prominent bulges seen inFIGS. 7 and 8 are the medial condyle 81 and lateral condyle 71, 82. Thefemoral intercondylar notch 83 lies between the condyles 81, 82; thelateral wall 72 of the intercondylar notch is exposed in FIG. 7. Theattachment areas of the anteromedial fibre bundle of the ACL 73 andposterolateral bundle 74 are seen. The whole attachment area 73, 74 ofthe ACL is elongated, inclined approximately 35-40 degrees from the axisof the femoral shaft 75. FIG. 8 is an end-view of the femur, as seen bythe surgeon when the knee is flexed 90 degrees. It is difficult to seethe ACL attachment 84 clearly in a true axial view, it being on thelateral side-wall of the notch. The region at the top of theintercondylar notch in FIG. 8 is known as the notch ‘roof’ 85. This isseen as a slightly curved line 76 in the midline section; the line isseen clearly on a medial-lateral radiograph, when it is known as‘Blumensaat's line’. The junction between the notch roof and theposterior aspect of the shaft of the femur 77 forms a transverse ridge78, that is easily located through the intercondylar notch 83. Thisridge may be used to locate an ACL drill guide, in a manner akin to thatused above, for the transverse interspinous ridge 11 of the tibia. Thecrest of this ridge is often referred to as the over-the-top position.This ‘posterior outlet’ of the intercondylar notch is nearlysemicircular, so surgeons may define a position around it in “o'clock”positions; 12 o'clock being at the top, etc. . . . Because the roof line76 of the notch is at an angle to the axis of the shaft of the femur 75,the roof 85 of the notch is seen sloping downwards in an end-view of thefemur. As the surgeon moves distally from the transverse ridge 78 i.e.towards the left in FIG. 7, the clock positions become less accurate, asthe roof 85 rises. Thus, an alternative method is to define the“o'clock” positions when looking through the notch 83 parallel to theslope of the roof line 76. Other means to define the attachmentpositions 73, 74 of the ACL bundles include fitting a circle to thecircular outline, as seen in the lateral direction, of the posteriorpart of the lateral femoral condyle 79 and navigating inanterior-posterior and proximal-distal directions from the centre of thecircle. The diameter may be defined as 100%, and the position of theattachment areas defined in percentage terms, thus normalising forvarious knee sizes. A further method is to define a reference grid onthe side wall of the notch, in this case by dividing the lateral sidewall of the notch into a rectangular grid as in FIG. 7 a. This referencegrid is then used to define the ACL attachment positions in percentageterms of height from the roof line 76 of the notch and distance alongthe notch roof from one end. In the example shown in FIG. 7 a,rectangular grid is defined having an upper side defined on the roofline 76, a lower side tangential to the bottom of the side wall 72 ofthe intercondylar notch, and proximal and distal ends also tangential tothe side wall 72 at the junction with the articular cartilage. In thisembodiment the grid is divided into sixteen zones, in four rows by fourcolumns. The zones are then numbered from one to sixteen starting withthe top section of the most proximal column, counting down that column,and then down successive columns, so that the lowest, most distal zoneis number 16.

One example of how the bony geometry may be used to locate a femoraltunnel drill guide is provided by the drill guide according to a furtherembodiment of the invention which is shown in FIGS. 9 and 10. Thisinstrument may include an angled probe tip 91 which has two locatingsurfaces 91 a, 91 b which are angled relative to each other to define alocating groove 91 c where they join. This forms a deep-shallow locatingmechanism arranged to locate on the transverse ridge 78 in theintercondylar notch 83. The probe tip 91 is joined to a curved sidepiece 101 which forms a high-low locating mechanism arranged to locateagainst the lateral side wall 72 and roof 85 of the intercondylar notch.The probe has formed through it, at one end of the curved side piece 101two drill guide apertures 93, 94 which are arranged to be located at thecentres of the ACL attachment areas 73, 74 when the locating mechanismsare located on their respective bone features. A handle 92 is attachedto the side piece 101 and is arranged to extend parallel to the femoralshaft when the probe is correctly located.

In use the angled probe tip 91 may be brought into contact with thetransverse ridge 78 at the posterior outlet of the intercondylar notch.This feature is common to many ‘offset’ drill guides. However, they donot control position around the notch, and the surgeon must make asubjective estimate of the correct “o'clock” position. In thisembodiment of the present invention, the side piece 101 is also locatedaround the lateral side-wall 72 of the notch. This provides fulllocation of the drill guide apertures 93, 94 in two dimensions on thesurface of the bone, and hence in three dimensions in total.

The probe may include only one hole rather than two if it is designedfor single bundle reconstruction.

In a further embodiment shown in FIG. 11, the angled probe tip 91 ofFIG. 9 is replaced by a curved locating extension 111, that is arrangedto wrap around the back surface 112 of the femoral condyle, so thatpulling the handle 92 will locate the drill holes 93, 94 correctly inthe shallow-deep direction as seen from the distal end of the femur. Itmay still incorporate a curved feature 101 that rests against the roofof the notch, in order to control the height of the drill holes.

Referring to FIG. 13 in another embodiment the handle 92 in FIG. 11 ismoved from the front of the knee so that, instead, the handle 131 isattached to the curved probe tip 112 at the end of the curved locatingextension 111, and will extend in the lateral direction when the probeis correctly located. The instrument may then be introduced from apostero-lateral incision in the manner shown in FIG. 13. The key featureof all these design variations is that the drilling target, representedby holes 93, 94, is always located in two dimensions across the surfaceof the bone at the area of the natural ACL attachment, i.e. shallow-deepand high-low as perceived by the surgeon.

In order to aid correct alignment of the intra-articular part of thedrill guide, the handle 52 for tibia, 92 for femur, will be adapted toaid the surgeon's perception of orientation. The graft tunnels arenormally drilled at compound angles to the axes of the bones, i.e.offset from both the anterior-posterior direction and offset from theperpendicular to the main longitudinal axis of the bone. This is forreasons of surgical access, avoiding vulnerable anatomical structures,and maintaining sufficient tunnel length. In the tibia, the tunnels arenormally drilled from outside-in, in approximately the orientationsshown in FIGS. 5 and 6. That is, so that they enter the tibia on theantero-medial aspect, from a point typically 2-6 cm distal to the tibialplateau, angled at approximately 40-60 degrees elevation, so that thetunnels are centred within the ACL attachment areas as desired. Asimilar situation occurs at the femur, except that the tunnels can bedrilled inside-out or outside-in. For inside-out drilling, the knee isusually flexed as far as possible and the guidewire is introduced intothe knee through an antero-medial portal, beside the patellar tendon. Itthen slants across the interior of the knee to the target holes 93, 94,passes through them and is then drilled into the lateral femoralcondyle, along the paths shown by way of example as 95 in FIGS. 9 and102 in FIG. 10, often until it emerges on the antero-lateral aspect ofthe thigh. In a similar inside-out method, the guidewire is passed intothe knee through a tibial graft tunnel that has been drilled first. Forinside-out femoral drilling, the surgeon may simply place the tip of theguidewire through holes 93, 94 by hand; no drill guide is needed.Conversely, for outside-in femoral drilling, the instrument body must beextended so that it passes around, from handle 92 or 131, to the lateralaspect of the knee. Here, there must be guide tubes or barrels, akin tothose 55, 56 shown in FIGS. 5 and 6, to ensure that the guidewire passesalong a fixed axis 95, 102 through the femur until it emerges into theknee joint at the desired graft attachment point 73, 74 and then maypass into hole 93, 94 in the locating piece within the knee.

In order to ensure that the intra-articular parts of the instrumentshave the correct alignment in the knee, the handles that enter the kneefrom the anterior aspect 52, 92 will be adapted to aid alignment. Thiswill depend on the surgeon's perceptions of symmetry and of parallelism.In some embodiments, the instrument includes an alignment member orhandle 62 attached to the probe so that, when it is held parallel to thelong axis of the tibia, as shown in FIG. 6, with the knee at a fixed 90degrees flexion angle, and on the midline sagittal plane i.e. so that itis directly in front of the tibia as can best be seen in FIG. 14, thenthe intra-articular parts 51, 61 will have the correct orientation. Thiswill particularly aid control of the “o'clock” position of locating part101 of the femur drill guide and, hence, the height of the drill holes93, 94 for attaching the reconstructed ligament to the femur as seen inFIG. 9.

In one embodiment as shown in FIG. 14, the handle 52 of a tibial drillguide incorporates a curved or angled part 141, that is arranged to passaround, i.e. to one side of, the patellar tendon 12 when the probe tipis in the correct position for drilling and the alignment handle 62 islocated on the anterior midline of the tibia. The curved part 141incorporates three angles or bends 142-144. A similar arrangement may beused to ensure the correct orientation of the femoral intra-articularinstrument, with or without drill guides held in fixed relationships toit for outside-in drill axis control.

This embodiment therefore incorporates bends, so that the handle passesaround the patellar tendon. The handle is brought onto the midline sothat it can be used to control/judge the orientation.

If the instrument is arranged to be introduced into the knee from theposterolateral direction as shown in FIG. 13, then it may be adapted bya joining part that passes around the lateral aspect of the knee to theanterior aspect, there joining to a handle arranged to be alignedparallel to the axis of the tibia similar to that of FIG. 14.

Referring to FIG. 15 a further embodiment of the invention comprises acomputer controlled navigation system for guiding a surgeon in the useof a drilling guide. This system comprises a drilling guide 100comprising a probe 102 with two drill guide apertures 104, 106 throughit, and two drill guide tubes 108, 110 supported in alignment with theguide apertures 104, 106 in a similar manner to the guide of FIG. 6. Theprobe 102 of the drill guide has a number of locating markers 112attached to it and a locating system 114 is provided that can locate theabsolute positions of each of the markers 112 in space, and hence theposition and orientation of the probe. This could, for example, be theBrainLab (Germany) system that uses reflective markers and stereocameras. Similarly, the bones (femur and tibia) will have markers 113attached such that the computer can calculate their positions in 3Dspace. The locating system is connected to a computer 116 which in turnis connected to a display 118. The computer 116 has stored in it datadefining models of a range of different possible sizes and shapes offemur and tibia based on measurements of real bone samples. It isarranged to provide instructions on the display 118 to instruct thesurgeon.

In use, the system first provides instructions to the surgeon via thedisplay 118 to move the tip 102 a of the probe 102 to various points onthe bone that is to be operated on. These instructions can identify anumber of easily identifiable points on the bone that the surgeon cantouch with the probe tip 102 a, or they may just instruct the surgeon tomove the probe tip 102 a over the surface of parts of the bone. As theprobe is moved to different locations on the bone, the computer 116monitors the different positions of the tip 102 a of the probe andstores these as a set of position data. From this position data, thecomputer 116 is then arranged to build up a model of the surface of thebone to be operated on. This model includes a number of features whichcan be used to locate the desired positions of the drillings for ACLreconstruction, in this case including the positions of the spinousprocesses 4, 5, the inter-spinous fossa 6, the inter-spinous ridge 11 onthe tibia, and the condyles 81, 82, inter-condylar notch 83 and thetransverse ridge 78 on the femur. Clearly the more actual points on thebone surface that are located by the probe, the more accurate the modelof the bone will be.

Once the model has been defined, the computer is arranged to identifythe positions in real space of the bone features to be used for drillinglocation, and to determine from those positions the desired positions inreal space of the drillings. This is done using stored data relating tothe actual positions of the ACL attachments, relative to the selectedbone features, on the femur and tibia for a number of bone samples. Fromthese desired drilling positions and data stored in the computerrelating to the shape of the probe and the positions of the drill guideapertures in the probe, the computer 116 determines the desired positionin real space for the drill guide 102 to guide a drill or guide wire tothe desired locations on the bone. The computer 116 then generates animage 120, with guide outputs in the form of guide markings 122 on itindicating the desired position of the guide 102, and guide positionmarkings 124 showing the actual position of the guide 102. In this casetwo images 120 are generated and displayed simultaneously showing thebone and probe 102 from different angles so that the surgeon can betterdetermine the absolute position of the probe relative to the desiredposition. By watching the images on the display 118 the surgeon can movethe guide 100 until the guide position markings 124 indicate that theguide 100 is in the desired position. The guide 100 can then be heldstill while the drillings are made.

Another variant of this system will have a single probe 100 that hastracking markers 112 used solely to digitise the bone features and notfeaturing drill guides. When the bone geometry has been determined, adrill with tracking features attached is placed on the outer surface ofthe knee. An image on the computer screen guides the surgeon such thatthe drill is oriented towards the correct attachment position within theknee.

The features selected for locating the drilling positions are selectedto provide location in two dimensions on the surface of the bone. Forexample the same features can be used for the tibia and the femur asdescribed above to provide physical location of the probe. However, itwill be appreciated that with this type of system the method of locatingthe desired position of the drillings on the surface of the bone can beconsiderably more complex than using two distances or angles fromrespective landmark features. For example the ideal drilling positioncan be defined by an optimisation process that determines an optimumposition using a large number of different distances and directions froma number of different points on the bone. However, such a locationmethod will still enable the optimum drilling position to be defined intwo dimensions on the bone surface.

In a further embodiment, the model of the bone is derived not fromcontact with a probe but by means of an imaging system which includes anumber of imaging devices, such as fluoroscopic imaging devices arrangedto image the knee joint from different angles. This allows a3-dimensional computer model of the bone to be built up which can beused to determine the optimum drilling positions and therefore theoptimum drill guide position. Guide markings can then be superimposed onthe image to indicate to the surgeon where the drill guide should belocated, and a real-time image of the actual probe used can then beprovided and monitored by the surgeon to determine when the probe is inthe desired position.

Measurement of Femoral ACL Attachment

In order to determine the optimum locations of drillings for attachingreconstructed ACLs a number of measurements of cadaver knees were taken.The aim was to describe the anatomical locations of the femoralattachment of the anterior cruciate ligament, for both its anteromedialAM and posterolateral PL bundles so that the drillings can be placed incorresponding locations. A number of different measurement techniqueswere used to achieve the most information concerning the attachment ofthe ACL.

22 human cadaver knees with intact anterior cruciate ligaments weremeasured. The femoral attachments of the two bundles were identified andmarked. Digital photographs were taken and the attachments were measuredand described in terms of the o'clock positions parallel to the femorallong axis and parallel to the roof of the intercondylar notch. Thecentres of the bundles were measured in a high-low and asuperficial-deep manner referencing from the centre of the posteriorfemoral condyle, and with respect to their positions within a referencegrid system as shown in FIG. 7 a. When looking parallel to the notchroof, the bulk of the AM bundle was attached between 9 and 11 o'clockand the bulk of the PL bundle between the 8 and 9.30 o'clock positions.The AM bundle was consistently found in zone 1 of the quadrant methodand the PL bundle in zone 7. Using the diameter of the posterior femoralcondyle reference method, the centre of the AM bundle should preferablybe located in the range 60 to 75% in a shallow-deep direction and in therange 45-60% in a high-low direction. The PL bundle should preferably belocated in the range 40-70% in a shallow-deep direction, and 40-70% in ahigh-low direction. The attachment was orientated at 37° to the femorallong axis.

Measurement of Tibial ACL Attachment

The aim was to find a measurement method that would lead to the mostconsistent placement of tibial tunnels for arthroscopic ACLreconstruction. This should be based on a reliable anatomic landmark toavoid a wide variation in positions between knees. It was found thatthis could be done by measuring from the “over-the-back” position, i.e.the top of the transverse inter-spinous ridge, in an anterior direction,and from the lateral surface of the medial tibial spine in a lateraldirection.

55 specimens were used and the anterior cruciate ligament attachmentswere measured in relation to various bony landmarks. Wide variation inmeasured values was found when using the posterior tibial axis, theanterior tibial surface and the tip of the medial tibial spine asreference points. The least variation in measured values occurredbetween the tibial interspinous “over-the-back” position and theposterior limit of the anterior cruciate ligament attachment. Theover-the-back landmark also led to the least variation in values withrespect to the centres of the fibre bundles. The attachments of theposterolateral and anteromedial bundles were 8 to 12 mm and 12 to 20 mmrespectively anterior to the over-the-back landmark and in the range of3 to 7 mm lateral to the lateral face of the medial tibial spine. Inorder to avoid notch impingement in the extended knee, the graft tunnelsshould be placed posteriorly in the ACL tibial fibre bundles; the PLtunnel in the range 8 to 10 mm and the AM tunnel 14 to 19 mm anterior tothe transverse intercondylar ridge. In relation to the posterior tibialaxis, these measurements are 24 to 35 mm for the PL bundle and 31 to 44mm for the AM bundle attachment. The corresponding tunnels should be inthe ranges 23 to 34 mm for the PL and 30 to 44 mm for the AM tunnel. Thedistances from the posterior surface of the tibia and the“over-the-back” position to the centres of the bundle attachmentscorrelated significantly with the ML width and the AP depth of thetibial plateaux, as did the distances to the centres of the tunnelpositions.

1. Apparatus for locating an attachment position for a reconstructed anterior cruciate ligament on an attachment surface of a bone, the bone having at least one reference surface, the apparatus comprising locating means arranged to locate the at least one reference surface and guide means arranged to define the attachment position in two dimensions on the attachment surface relative to the at least one reference surface.
 2. Apparatus according to claim 1 wherein the bone has first and second reference surfaces and the locating means is arranged to locate the first and second reference surfaces of the bone to provide location of the attachment position in first and second dimensions.
 3. Apparatus according to claim 1 wherein the attachment surface is arranged to provide location in a third dimension thereby to define the attachment position in three dimensions.
 4. Apparatus according to any foregoing claim arranged to locate an attachment position on a tibia.
 5. Apparatus according to claim 4 wherein the tibia has an inter-spinous ridge and the locating means is arranged to locate the inter-spinous ridge.
 6. Apparatus according to claim 4 wherein the tibia has a spinous process which has lateral and medical aspects and the locating means is arranged to locate one of the aspects.
 7. Apparatus according to claim 4 wherein the tibia has a posterior tibial trans-condylar axis and the locating means is arranged to locate the posterior tibial trans-condylar axis.
 8. Apparatus according to claim 4 wherein the tibia has a tibial plateau and the locating means is arranged to locate an edge of the tibial plateau.
 9. Apparatus according to claim 1 arranged to locate an attachment position on a femur.
 10. Apparatus according to claim 9 wherein the femur has a femoral intercondylar notch having a posterior edge and transverse ridge at the posterior edge and the locating means is arranged to locate on the transverse ridge.
 11. Apparatus according to claim 9 wherein the femur has a femoral intercondylar notch having a roof and a side wall and the locating means is arranged to locate on at least one of the roof and the side wall.
 12. Apparatus according to claim 9 wherein the femur has a femoral condyle having a posterior proximal aspect and the locating means is arranged to locate on the posterior proximal aspect of the femoral lateral condyle.
 13. Apparatus according to claim 1 wherein the guide means is arranged to define two attachment positions for respective fibre bundles.
 14. Apparatus according to claim 1 which comprises an instrument wherein the locating means comprises a locating surface arranged to contact the reference surface.
 15. Apparatus according to claim 14 wherein the bone has two reference surfaces and the locating means comprises two locating surfaces each arranged to locate on a respective one of the reference surfaces.
 16. Apparatus according to claim 14 wherein the locating surface is formed in two parts angled at from 45° to 60° to each other.
 17. Apparatus according to claim 14 wherein the instrument comprises a probe including the guide and an alignment means connected to the probe and arranged to aid alignment of the probe.
 18. Apparatus according to claim 17 wherein the alignment means is arranged to define an alignment axis which is arranged to be aligned with an anatomical feature of the patient when the guide is correctly aligned.
 19. Apparatus according to claim 18 wherein the alignment member is elongate.
 20. Apparatus according to any of claim 17 wherein the alignment member is arranged to be aligned with the long axis of a bone of the patient when the guide is correctly aligned.
 21. Apparatus according to claim 17 wherein the alignment member is connected to the probe by a support that includes an offset portion arranged to extend around an anatomical feature of the patient when the guide is correctly aligned.
 22. Apparatus according to claim 1 wherein the locating means is arranged to locate the reference surface from data relating to the position of a part of the bone.
 23. Apparatus according to claim 22 wherein the guide is arranged to define a target position for a guide device and to provide guidance outputs arranged to enable a user to place the guide device in the target position.
 24. A method of locating an attachment position for a reconstructed anterior cruciate ligament on an attachment surface of a bone, the method comprising locating at least one reference surface of the bone and defining the attachment position in two dimensions on the attachment surface relative to the reference surface. 